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Chemistry 481(01) Spring 2014

Chemistry 481(01) Spring 2014. Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu Office: CTH 311 Phone 257-4941 Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th , F 10:00 - 12:00 a.m . April 10 , 2014: Test 1 (Chapters 1,  2, 3,)

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Chemistry 481(01) Spring 2014

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  1. Chemistry 481(01) Spring 2014 • Instructor: Dr. Upali Siriwardane • e-mail: upali@latech.edu • Office: CTH 311 Phone 257-4941 • Office Hours: • M,W 8:00-9:00 & 11:00-12:00 am; • Tu,Th, F 10:00 - 12:00 a.m. • April 10 , 2014: Test 1 (Chapters 1,  2, 3,) • May 1, 2014: Test 2 (Chapters  5, 6 & 7) • May 20, 2014: Test 3 (Chapters. 19 & 20) • May 22, Make Up: Comprehensive covering all Chapters

  2. Origin of Elements in the Universe Scientists have long based the origin of our Universe on the Big Bang Theory. According to this theory, our universe was simply an expanding fairly cold entity consisting of only Hydrogen and Helium during it's incipient stages. Over the expanse of many years, and through a continuing process of fusion and fission, our universe has come to consist of numerous chemical elements, four terrestrial planets(Earth,Mars, Venus, and Mercury), and five giant gas planets(Saturn, Jupiter, Neptune, Pluto, and Uranus).

  3. Predicted Nuclear Fusion ofLight Elements in the Young,Hot Universe

  4. Few minutes after big Bang

  5. Eight Steps in the History of the Earth 1. The Big Bang 2. Star Formation 3. Supernova Explosion 4. Solar Nebula Condenses 5. Sun & Planetary Rings Form 6. Earth Forms 7. Earth's Core Forms  8. Oceans & Atmosphere Forms

  6. Nuclear Burning

  7. Origin of the Elements: Nucleosynthesis • Elements formed in the universe's original stars were made from hydrogen gas condensing due to gravity. These young stars "burned" hydrogen in fusion reactions to produce helium and the hydrogen was depleted. Reactions such as those below built up all the heavier elements up to atomic number 26 in the periodic table. • When the stars got old they exploded in a super nova, spreading the new elements into space with high flux of neutrons to produce heavy elements by neutron capture.

  8. 1. What are the two basic types of nuclear reactions? Give examples of each that occur during the formation of the Universe

  9. Cosmic Abundances

  10. Balancing Nuclear Reactions Two conditions must be met to balance nuclear reactions: 1. The sum of the masses of the reactants must equal the sum of the masses of the products. (i.e., the values of A must balance on both sides of the equation.) 2. The sum of the protons for the reactants must equal the sum of the protons for the products. (i.e., the values of Z must balance on both sides of the equation.)

  11. Balancing Nuclear Reactions 2. Complete the following Nuclear reactions: • Uranium – 238 decays by alpha radiation to produce what other element? • Uranium – 238 decays by alpha radiation to produce what other element? • What element did we start out with if the result of beta decay is bismuth– 214?

  12. Balancing Nuclear Reactions 2. Complete the following Nuclear reactions: d) What element is produced when mercury – 201 captures an inner shell electron with the production of a gamma ray to release excess energy?

  13. 3. Predict the most likely modes of decay and the products of decay of the following nuclides: 17F: 105Ag:     185Ta:

  14. Bonding Energy Curve

  15. Nuclear Binding Energy The binding energy of a nucleus is a measure of how tightly its protons and neutrons are held together by the nuclear forces. The binding energy per nucleon, the energy required to remove one neutron or proton from a nucleus, is a function of the mass number A. (Dm) –mass defect (Dm) = Mass of Nuclide - mass of (p + n +e ) Proton mass: 1.00728 amu Neutron mass: 1.00867 amu Electron mass: 0.00055 amu Massdefect (Dm), then multiply by 931.5 MeV/amu

  16. 4. Using the binding energy calculator, calculate the binding energy 235U if the mass of the this nuclide (isotope) is 235.0349 amu. ( P= 1.007277 amu, N= 1.008665 amu, e- =0.0005438 amu )

  17. 5. What are theories that have been used to describe the nuclear stability?

  18. Stability of the Elements and Their Isotopes P/N Ratio Why are elements With Z > 82 are Unstable?

  19. Magic Numbers • Nuclei with either numbers of protons or neutrons equal to Z, N =2 (He), 8(O), 20 (Ca), 28(Si), 50(Sn, 82(Pb), or 126(?)(I) • exhibit certain properties which are analogous to closed shell properties in atoms, including • anomalously low masses, high natural abundances and high energy first excited states.

  20. The Kinetics of Radioactive Decay Nuclear reactions follow 1st order kinetics

  21. 6. How long would it take for a sample of 222Rn that weighs 0.750 g to decay to 0.100 g?  Assume a half-life for 222Rn of 3.823 days?

  22. 7. The skin, bones and clothing of an adult female mummy discovered in Chimney Cave, Lake Winnemucca, Nevada, were dated by radiocarbon analysis.  How old is this mummy if the sample retains 73.9% of the activity of living tissue?

  23. =( ) 1 nf2 1 ni2 - Bohr model of the atom Balmer later determined an empirical relationship that described the spectral lines for hydrogen. DE = - 2.178 x 10-18 m-1 nf = 2 ni = 3,4, 5, . . . Blamer series Spectra of many other atoms can be described by similar relationships.

  24. Bohr model of the atom • The Bohr model is a ‘planetary’ type model. • Each principal quantum represents a new ‘orbit’ or layer. • The nucleus is at the center of the model. • RH = 2.178 x 10-18 J En = RH En = -

  25. Emission Spectrum of Hydrogen • Bohr studied the spectra produced when atoms were excited in a gas discharge tube. He observed that each element produced its own set of characteristic lines.

  26. Emission Spectrum of Hydrogen • Line Spectrum • Energy is absorbed when an electron goes from a lower(n) to a higher(n) • Energy is emitted when an electron goes from a higher(n) to a lower(n) level • Energy changed is given by:DE = Ef - Ei • or DE = -2.178 x 10-18 [1/n2f - 1/n2i] J • DE is negative for an emission and positive for an absorption • DE can be converted to l or 1/ lby l = hc/E.

  27. What is Bohr’s Atomic model? • explain emission spectrum of hydrogen atom • applied the idea of Quantization to electrons to orbits • energies of these orbits increase with the distance from nucleus. • Energy of the electron in orbit n (En): • En = -2.178 x 10-18 J (Z2/n2) • En = -2.178 x 10-18 J 1/n2; Z=1 for H

  28. ( ) 1 ni2 1 nf2 - Bohr model of the atom Balmer later determined an empirical relationship that described the spectral lines for hydrogen. En = - DE = - 2.178 x 10-18J nf = 2 ni = 3,4, 5, . . . Blamer series Spectra of many other atoms can be described by similar relationships.

  29. Paschen, Blamer and Lyman Series

  30. Calculation using the equation: E = -2.178 x 10-18 (1/nf2 - 1/ni2 ) J, Calculate the wavelength of light that can excite the electron in a ground state hydrogen atom to n = 7 energy level.

  31. Calculation using Bohr eqaution The energy for the transition from n = 1 to n = 7: DE = -2.178 x 10-18 J [1/n2f - 1/n2i]; nf = 7, ni = 1 DE = -2.178 x 10-18 [1/72 - 1/12] J DE = -2.178 x 10-18 [1/49 - 1/1] J DE = -2.178 x 10-18 [0.02041 - 1] J DE = -2.178 x 10-18 [-0.97959] J = 2.134 x 10-18 J (+, absorption) calculate the l using l = hc/E 6.626 x 10-34 Js x 3.00 x 108 m/s l = ---------------------- 2.13 x 10-18 J l = 9.31 x 10-8 m

  32. 8. Using Bohr energy calculator, calculate the wavelength of light that can excite the electron in a ground state hydrogen atom from n = 5 to n = 3 energy level.

  33. Wave theory of the electron • 1924:De Broglie suggested that electrons have wave properties to account for why their energy was quantized. • He reasoned that the electron in the hydrogen atom was fixed in the space around the nucleus. • He felt that the electron would best be represented as a standing wave. • As a standing wave, each electron’s path must equal a whole number times the wavelength.

  34. h mv l = De Broglie waves De Broglie proposed that all particles have a wavelength as related by: l = wavelength, meters h = Plank’s constant m = mass, kg v = frequency, m/s

  35. Constructively Interfered 2D-Wave

  36. destructively Interfered 2D-Wave

  37. Two-dimensional wave - Vibrations on a Drumskin One circular node (at the drumskin's edge) Two circular nodes (one at the drumskin's edge plus one more) Three circular nodes (one at the drumskin's edge plus two more) One transverse node (plus a circular one at the drumskin's edge) Two transverse nodes (plus one at the drumskin's edge)

  38. What is a wave-mechanical model? • motions of a vibrating string shows one dimensional motion. • Energy of the vibrating string is quantized • Energy of the waves increased with the nodes. • Nodes are places were string is stationary. • Number of nodes gives the quantum number. One dimensional motion gives one quantum number. Vibrating String : y = sin(npx/l) d2y/dx2 = -(n2p2/l2)sin(npx/l) = -(n2p2/l2)y

  39. Quantum model of the atom • Schrödinger developed an equation to describe the behavior and energies of electrons in atoms. • His equation ( Wave function ) is similar to one used to describe electromagnetic waves. Each electron can be described in terms of Wave function its quantum numbers. n, l, ml, ms), • 2 is proportional probablity of finding the electron in a given volume. Max Born Interpretation: 2 = atomic orbital

  40. Schrödinger Equation  = wave function E = total energy V = potential energy

  41. Schrödinger Equation  = wave function E = total energy V = potential energy

  42. Schrödinger Equation in Polar Coordinates

  43. Polar Coordinates

  44. Quantum Model of atom • Electrons travel in three dimensions • Four quantum numbers are needed • three to describe, x, y, z, and four for the spin • four quantum numbers describe an orbital currently used to explain the arrangement, bonding and spectra of atoms.

  45. Four Quantum Numbers of the Atom • n value could be 1, 2, 3, 4, 5, 6. 7. . . etc. • l values depend on n value: can have 0 . . . (n - 1) values • ml values depends on l value: can have -l . , 0 . . . +l values of ml • ms values should always be -1/2 or +1/2

  46. Solutions to Shrődinger Equation Series of allowed discrete  values: n, l, ml, ms n = 1,2,3,4,5,6,7..etc. En = -

  47. Components of  Mathematical expression of hydrogen like orbitals in polar coordinates: n, l, ml, ms (r,,) = R n, l, (r)Y l, ml, (,) R n, l, (r ) = Radial Wave Function Y l, ml, (,) =Angular Wave Function [R n, l (r )]2 or 4pr2R2 = Radial Distribution Function or Pnl(r).

  48. Radial Distribution Function, Pnl(r). This is defined as the probability that an electron in the orbital with quantum numbers n and l will be found at a distance r from the nucleus. It is related to the radial wave function by the following relationship: ; normalized by

  49. 9. Describe the Schrödinger equation and the breaking up of wave function,  into radial and angular component of a wave function and explain the general rule used to find the number of radial and angular nodes of a wave function.

  50. s-Atomic Orbitals R n, l, (r) only no Y l, ml, (,) s orbitals

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